The present invention relates to curable polyacetoacetate resins and more particularly relates to such resins which require relatively low solvent loading.
U.S. Pat. No. 3,668,183 describes a polyenamine resin produced from the reaction between polyacetoacetates or polyacetoamides with blocked polyamines. The patent generically discloses at least 30 possible diamines to be blocked and 26 carboxyl compounds to be used for blocking. This yields 780 possible combinations if blends are not used. If blends are used, over 20,000 combinations are possible. In general, the polyamine is blocked with an aliphatic ketone or aldehyde to form ketimines or aldimines. All specific examples utilize aliphatic ketones as blocking agents. The only ketone aromatic compound even suggested for blocking within a long list of possible blocking agents, is the aromatic ketone methyl phenyl ketone. The only aromatic aldehyde suggested for blocking is benzaldehyde and no advantage is suggested for its selection from among the long list of other possibilities.
According to U.S. Pat. No. 3,668,183, the reaction proceeds by water hydrolysis of the ketimine or aldimine to regenerate the amine which then reacts with the polyacetoamide and polyacetoacetate. The reaction and product of U.S. Pat. No. 3,668,183 has significant disadvantages. In particular, coatings or films can be formed only in relatively thin layers due to the requirement of atmospheric moisture penetration in order to cure the coating or film. Furthermore, the system is exceedingly moisture intolerant and the ketimine or aldimine compound must be carefully protected from moisture. In addition, because the system requires moisture penetration, uniform curing throughout a coating is difficult, thus gloss and solvent resistance is often not as high as desired. Also, since the system is dependent upon external moisture, which is a variable, cure times and cure properties are not consistent.
U.S. Pat. No. 4,772,680 and European Patent Application 0199087 similarly describe a reaction between acetoacetate and aliphatic amines blocked with aliphatic or cycloaliphatic ketones. These systems again rely upon hydrolysis to catalyze the reaction and are thus subject to all the disadvantages previously described with respect to U.S. Pat. No. 3,668,183.
It is known that aromatic aldehydes are so reactive to primary amines that imines form at room temperature, even without removal of water of reaction. This indicates that aromatic aldimines are relatively stable to hydrolysis, and are thus not suitable for a water catalyzed reaction such as described in the forgoing references, despite the suggestion of U.S. Pat. No. 3,668,183 to the contrary.